1. Field of the Invention
The present invention relates to a dielectric ceramic composition for use in multilayer ceramic parts and the like, a method for manufacture thereof and a multilayer ceramic part using the composition.
2. Description of the Related Art
With the recent reduction in size and thickness of electronic parts, there is an increasing need for multilayer ceramic parts. A typical multilayer ceramic part includes, in each layer thereof, an inductor or capacitor circuit formed by using a low-temperature co-fired ceramic (LTCC) which is co-firable with a conductive material such as Ag. Generally, a dielectric ceramic composition containing alumina or other ceramic filler and a glass is used as the low-temperature co-fired material for use in multilayer ceramic parts. However, such a composition has a low dielectric constant of 10 or below and, when applied to an LC filter, shows insufficient dielectric characteristics.
In order for a dielectric ceramic composition to be applicable to an LC filter, it must exhibit a high dielectric constant, a low dielectric loss and a temperature coefficient τf of approximately 0. As a composition which meets such characteristics, a dielectric ceramic composition having a composition of Li2O—CaO—Sm2O3—TiO2 is disclosed in Japanese Patent Laying-Open No. Hei 5-211007.
Also, Japanese Patent Laying-Open No. 2003-146742 discloses a dielectric ceramic composition containing (Li0.5 (Nd, Sm)0.5)TiO3—(Ca1-xNd2x/3)TiO3 and 3–15% by weight of a ZnO—B2O3—SiO2 based glass frit or an Li2O—B2O3—SiO2 based glass frit.
However, the dielectric ceramic composition disclosed in Japanese Patent Laying-Open No. Hei 5-211007 is fired at a high temperature of about 1,300° C. and its original composition has made it difficult to be applied to multilayer ceramic parts which require firing at a low temperature of about 900° C.
The dielectric ceramic composition disclosed in Japanese Patent Laying-Open No. 2003-146742 needs to increase its glass loading in order to improve sinterability at a low temperature of about 900° C. The increased glass loading however results in deterioration of dielectric characteristics, which has been a problem.
Also, it is reported in Jpn. J. Appl. Phys., Vol. 32, pp. 4319–4322 that if Ln is Tb in the CaO—Li2O-Ln2O3—TiO2 ceramic, a perovskite phase precipitates as a main phase and Ln2Ti2O7 additionally precipitates as a second phase. This second phase is responsible for the reduction in Qf value. The ceramic disclosed therein excludes a glass component and is not a dielectric ceramic composition firable at low temperatures.